Method for making a die for roll forming a dual threaded bolt

Abstract

The die forming process includes first passing a circular coarse thread cutter over the forming surface of the die at an angle away from parallel to a side edge matching a pitch for coarse threads to be formed by the die. The coarse thread cutter is truncated with a notch within a flattened tip, the notch forming upper portions of crests in the forming surface of the die. A fine thread cutter of circular form is then utilized to cut portions of the root of the dual threaded die. The fine thread cutter is angled relative to side edges of the die at an angle substantially half of an angle at which the coarse thread cutter is angled. The fine thread cutter cuts at a variable depth as the fine thread cutter advances along the root between the crests to form flanks of a bridge within the root.

What is claimed is: 
     
       1. A method for making a die for roll forming a dual threaded bolt, the die forming method including the steps of:
 identifying a block of die forming material having a substantially flat forming surface between a pair of opposing side edges and opposing lead and rear edges; 
 cutting the forming surface to form upper portions of a series of parallel coarse thread crests with tapered sides, by using a truncated coarse thread cutter having a circular form with cutting teeth on a perimeter, the cutting teeth having a distal portion and a notch in the distal portion with tapering slopes matching a contour of the upper portions of the coarse thread crests, the notch of the truncated coarse thread cutter forming the upper portions of the coarse thread crests, the tapering slopes of the notch of the truncated coarse thread cutter forming the tapered sides of the coarse thread crests; and 
 further cutting the forming surface between the upper portions of the series of parallel coarse thread crests to form roots between the coarse thread crests, the roots including bridges therein angled relative to the crests and extending between adjacent crests, by using a fine thread cutter having a circular form with cutting teeth on a perimeter, the cutting teeth of the fine thread cutter having a tip between angled surfaces, the tip of the fine thread cutter narrower than the distal portion of the truncated coarse thread cutter, the tip and the angled surfaces of the fine thread cutter forming the roots and the bridges within the roots. 
 
     
     
       2. The method of  claim 1  wherein said further cutting step includes the angled surfaces of the tip of the fine thread cutter each having an angle which matches an angle of taper of the tapered sides of the coarse thread crests formed by the tapering slopes of the notch in the distal portion of the truncated coarse thread cutter of said cutting step.